Chemicals of interest have been tested for mutagenicity in Salmonella. The chemicals studied were sodium bisulfite, cyclic nitrosamines, glutathione, N-substituted phenanthreneimines, and p-nitrophenyl pentadienal (NPPD: "spy dust"). The mutagenicity of bisulfite appears to occur through a free-radical mediated mechanism, and the level of mutagenesis is dependent on the rate of autooxidation of the bisulfite ion. The mutagenicity of the nitrosamines in the presence of homogenates from various organs does not appear to be related to their organ specificity for carcinogenesis. Glutathione is mutagenic in Salmonella as a result of its metabolism by purified Gamma-glutamyl transferase. The mutagenicity of phenanthreneimines is related to the electron-attracting or releasing properties of the N-substituted moieties, and their alkylation via carbonium ions is inversely proportional to their mutagenicity. NPPD ("spy dust") and one of its metabolites is mutagenic in Salmonella. The mutagenicity appears to be dependent on nitroreduction by either bacterial or rodent liver nitroreductases.